Phenol-formaldehyde (PF) resins, as well as PF resins extended with urea (PFU resins), have been the mainstays of fiberglass insulation binder technology over the past several years. Such resins are inexpensive and provide the cured fiberglass insulation product with excellent physical properties.
Some of the drawbacks of this technology, however, are the potential for formaldehyde emissions during the manufacturing of the fiberglass insulation and the crystallization of bis (4-hydroxy-3,5-dimethylolphenol) methane (tetradimer) from the PF resin as its formaldehyde content is reduced below 3 percent. The tetradimer crystal phase is difficult to re-dissolve and contributes to a variety of processing problems not the least of which is plugging in piping and spraying equipment.
Fiberglass insulation is typically made by spaying a dilute aqueous solution of the PF or PFU resin binder onto a moving mat or blanket of non-woven glass fibers, often hot from being recently formed, and then heating the mat or blanket to an elevated temperature in an oven to cure the resin. As a result, free phenol and free formaldehyde in the resin can easily volatilize during use. Manufacturing facilities using PF and PFU resins as the main binder component for insulation products have had to invest in pollution abatement equipment to minimize the possible exposure of workers to such emissions and to meet Maximum Achieveable Control Technology (MACT) requirement Standards.
Higginbottom U.S. Pat. No. 4,028,367 describes an aqueous resole resin composition that is purportedly stable with respect to the unwanted crystallization of tetradimer (bis (4-hydroxy-3,5-dimethylol)methane)) and is low in free phenol and free formaldehyde. Such a resin would appear to be ideally suited for use in making fiberglass insulation.
In particular, the resole resin of the Higginbottom patent has a pH less than 8.5, contains less than 2 percent free phenol and less than 2 percent free formaldehyde and has a number average molecular weight of less than 300. The resole is prepared at a combined formaldehyde to phenol (F:P) mole ratio in the range of 2:1 to 2.9:1. In each of the Examples the combined F:P mole ratio was below 2.4.
According to the Higginbottom patent, this aqueous resole composition is prepared using a two-step process. First, a molar excess of phenol is reacted with formaldehyde (1 mole phenol with 0.05 to 0.3 mole formaldehyde) under an acidic condition sufficient to form a novolac resin. Thereafter, additional formaldehyde is added (broadly described as 1.75 to 3.5 moles per mole of original phenol), and reacted under basic conditions to yield the resole resin. In each of the Examples the total amount of formaldehyde actually added per mole of original phenol was below 3.0 moles. The level of free formaldehyde in the resole is then further reduced by adding a formaldehyde scavenger near the end of the resole reaction in an amount of 0.5 to 1.5 mole equivalents per mole of free formaldehyde. Urea is one of several options disclosed.
The novolac reaction step is conducted at a temperature broadly in the range of 60° to 200° C., depending on the catalyst used. A typical temperature is in the range of 100° to 120° C. Under these conditions, the patent indicates that a sizable population of 2,2′- and 2,4′-dihydroxydiphenylmethanes are produced along with the minor amounts of the 4,4′-dimer. The Higginbottom patent advises against using lower novolac reaction temperatures, as this produces a much greater amount of the less desirable 4,4′-dimer (See col. 3, lines 11-15).
In order to initiate the formation of the resole resin following the novolac chemistry, a base is added to neutralize any acid used in making the novolac and then 0.05 to 0.3 mole equivalent of additional base per mole of original phenol is added above the amount needed to neutralize the acid. The resole reaction is conducted at a temperature broadly in the range of 40° to 80° C. A preferred temperature is in the range of 50° to 70° C. and each of the Examples actually is prepared in the range of 60° to 70° C. These temperatures are said to provide an adequate rate of reaction without excessive oligomerization of the resole. At the end of the resole reaction, the base is neutralized to obtain an aqueous composition at a pH between 6 and 8.5, preferably between 7 and 8.
The larger amount of the methylolated 2,2′-hydroxy and the 2,4′-hydroxy diphenylmethane species purportedly produced by the Higginbottom process is said to help suppress crystallization of the tetradimer (bis (4-hydroxy-3,5-dimethylolphenyl)methane), allowing the level of free (unreacted) formaldehyde to be reduced almost completely in the resole, often through the use of a formaldehyde scavenger.
The resole resin obtained by the process of the Higginbottom patent is said to have a water tolerance in the range of 100 to 800 percent, i.e., haze occurs when an amount of water from 1 to up to about 8 times the amount (mass) of resole is added to the resin. It is this latter property that interferes with the widespread use of the Higginbottom resole resin for making fiberglass insulation.
Because it is preferred that the resole resins used in making a binder composition for producing glass fiber insulation be significantly diluted before use, it would be desirable to have a resole resin with improved water dilution properties relative to the prior art Higginbottom resole. The present invention accomplishes that goal, making the resole resin solution of this invention easier for glass fiber insulation plants to use.
The present invention accomplishes this result while avoiding the complications caused by tetradimer (bis (4-hydroxy-3,5-dihydroxymethylphenyl) methane) precipitation (crystallization) that generally accompanies resole resins made at elevated F:P mole ratios using traditional methods and at low levels of free formaldehyde. The low amount of tetradimer in the resole resin of the present invention results in binder compositions that avoid spray nozzle plugging problems and short shelf-life.
U.S. Published Patent Application 20010036996 describes a highly urea-extended phenol-formaldehyde (PF) resin wherein the PF resin is made at an initial formaldehyde to phenol molar ratio of greater than 3.75:1.